Key Democrats warn that if the president decides to send more troops to Afghanistan, they might oppose it, perhaps even moving to cut off funds for the buildup.

WASHINGTON — Key Democrats on Capitol Hill warned Thursday that a decision by President Obama to send more troops to Afghanistan could trigger an uprising within the party, possibly including an attempt to cut off funds for the buildup.

"I believe we need to more narrowly focus our efforts and have a much more achievable and targeted policy in that region," said Rep. David R. Obey (D-Wis.), chairman of the House Appropriations Committee. Otherwise, he said, "we run the risk of repeating the mistakes we made in Vietnam and the Russians made in Afghanistan."

Rep. John P. Murtha (D-Pa.), an influential voice on military affairs who is also on the committee, predicted a fight on the House floor if a request to fund a troop increase came to a vote.

"The public is worn out by war," Murtha said. "The troops, no matter what the military says, are exhausted."

Obey's and Murtha's comments were the strongest suggestions from congressional Democrats that Obama could face significant opposition if he follows Army Gen. Stanley A. McChrystal's recommendation to send up to 40,000 more U.S. troops to Afghanistan, in addition to the 68,000 already there, as part of a counterinsurgency strategy to keep the Taliban from regaining power. The lawmakers' statements came on a day when the president's national security advisor, James Jones, briefed House members on the situation.

A schism erupting among Democrats would present Obama with his first serious backlash within his party. That possibility may be a reason he reached out to congressional Republicans at a White House meeting this week.

Obama is in the midst of reviewing his administration's policy in Afghanistan. In addition to McChrystal's call for a troop buildup, options include expanding the Afghan army and narrowing the war effort to focus on Al Qaeda. Already, the administration says it is regarding the Taliban as a local movement, while Al Qaeda is a global threat to the United States.

Congressional Republicans have pressed Obama to approve McChrystal's troop request, casting the decision as a test of the president's commitment to the war.

But whereas Obey and Murtha have been openly critical of the idea, most Democrats have kept their views more closely held, saying they would await the president's decision before expressing an opinion.

During the George W. Bush administration, congressional Democrats attempted to use the budget to change the course of the Iraq war. They failed, with some Democrats joining Republicans to ensure that the troops remained fully funded. With a Democrat now in the White House, a public row with Congress would seem even less likely, unless the situation in Afghanistan deteriorated further.

In June, several war critics in the House tried to force the administration to produce an exit strategy. The measure failed, with some Democrats and almost all Republicans voting against it.

Obama is likely to need GOP support if his Afghan policy faces another vote. Murtha conceded as much Thursday.

"The House right now, I'm convinced, will vote for a supplemental [funding bill] for whatever he asks for," he said. "It won't be easy. And it may not have a majority of Democrats."

"If Bush was still in power, there would be much less support. We trust Obama that if we give him resources to accomplish a particular mission in a particular way, that's what he will do," Sherman said.

Senate Majority Leader Harry Reid (D-Nev.) said that his caucus would support Obama's decision. Still, a troop expansion could encounter fierce criticism.

Sen. John F. Kerry (D-Mass.), the chairman of the Senate Foreign Relations Committee, is traveling to Afghanistan next week to review the situation. If he reaches a different conclusion than Obama, aides say, Kerry will use his committee to push the administration to explain itself.

Sen. Carl Levin (D-Mich.), chairman of the Armed Services Committee, has also expressed concern about a troop buildup. But this week, Levin said he hoped the president would find a compromise that would satisfy most lawmakers.

"I don't think anybody wants to preclude the possibility that there could be strong bipartisan support for that decision before it's made," Levin said.

Aides close to the Democratic leadership say it is unlikely to coalesce around a single position.

Sen. Russell D. Feingold (D-Wis.), a member of both the Senate foreign relations and intelligence committees, has emerged as a fierce critic of McChrystal's recommendation. Feingold favors a timetable for withdrawal and says if Obama decides to send more troops, Congress should contest it.